The present invention relates to a plate thickness detection method, a plate thickness detector, a reference inter-blade distance detection method, and a reference inter-blade distance detector for a bending machine for bending a workpiece by causing a punch to make a relative stroke and to cooperate with a die in the bending.
In addition, the present invention relates to a bending method and a bending apparatus for directly detecting the relative stroke value of a punch to a die and controlling the relative stroke of the punch by a vertically movable displacement gauge which is provided in the die and protruded from the V groove of the die.
The present invention also relates to a bending method and a bending apparatus capable of conducting accurate bending by calculating a D-value in light of a change in the plate thickness of a workpiece which is generated during the bending.
According to conventional bending, a nominal plate thickness is input to an NC device and a D-value for a desired bending angle is thereby calculated. An actual plate thickness, however, varies according to the difference in manufacturer or a lot and a desired angle cannot be often obtained.
Considering this, as disclosed in Japanese Patent Application Laid-Open No. 63-157722, the relative pressure of a punch against a die from the torque of a servo motor elevating a ram is measured, and a position corresponding to a rising point of torque is considered as a workpiece upper position so as to detect a plate thickness.
Further, as disclosed in Japanese Patent Application Laid-Open No. 6-74746, a plate thickness is measured by setting a point at which the difference between a linear scale value and an NC device instruction value occurs based on the backlash of a ball screw which drives a ram, as a reference point at which a punch contacts with a workpiece.
However, in the method disclosed in 63-157722, it is disadvantageously difficult to detect the rising of pressure for a thin workpiece.
Further, as in the case of the method disclosed in 6-74746, if a point at which the difference between a linear scale value and an NC device instruction value occurs based on the backlash is determined as a point at which a punch contacts with a workpiece, xe2x80x9can excessive lashxe2x80x9d which causes a backlash to enable detection is necessary. This makes it disadvantageously impossible to apply this method to a hydraulic bending machine.
Meanwhile, as shown in FIG. 1, if a workpiece W is bent by a punch P and a die D cooperatively in a press brake, for example, as a bending apparatus, a ram position detection means 103 for detecting the upper and lower positions of a ram 101 is provided so as to measure the distance between the punch P and the die D to thereby obtain a predetermined bending angle. A D-value is calculated in light of die conditions, workpiece conditions and the like, the ram position detection means 103 controls the D-value to bend the workpiece W.
However, even if the predetermined D-value is calculated and the relative distance of the punch P to the die D is controlled to obtain the D-value, mechanical deflections such as the deflections of side plates, those of upper and lower tables and that of the die occur due to the bending reaction of the workpiece W during the bending. Unless these deflections are corrected, bending with accurate angle cannot be ensured. However, it is quite difficult to accurately calculate and correct these mechanical deflections.
To solve this, as disclosed in, for example, Japanese Utility Model Application Publication No. 6-49374, there is proposed a bending method for directly detecting a D-value without the need to consider mechanical deflections. That is, as shown in FIG. 2, this position detection means 105 has a vertically movable detection pin 109 protruded from a V groove 107 of a die D and provided in the die D to be always urged upward, and detects the vertical movement of the detection pin 109 using a displacement gauge 111.
Therefore, if a punch P descends to thereby bend the workpiece W downward, then the lower surface of the workpiece W which is being bent is abutted on the detection pin 109 to press the pin 109 down. The descent of the detection pin 109 is detected by the displacement gauge 111 to thereby directly detect a D-value.
Even with the conventional art, however, it is difficult to accurately calculate the relative stroke value of the punch P to obtain a target bending angle because of the various characteristics of the workpiece W, e.g., spring-back by which if the workpiece W is unloaded after being bent, the bending angle recovers.
On the other hand, with both the method shown in 63-15772 and that shown in 6-74746 as described above, a phenomenon that the actual plate thickness of the workpiece changes (decreases) during bending occurs. According to each method, the D-value is calculated not in light of the decrease of the thickness but based on the detection of the position at which the punch contacts with the workpiece at the start of bending. Since the D-value is not calculated in light of the thickness change (decrease) after the bending completely starts, the method has a disadvantage in that a target angle cannot be accurately obtained.
The present invention has been made while paying attention to the above-stated conventional disadvantages and the object of the present invention is to provide a plate thickness detection method, a plate thickness detector, a reference inter-blade distance detection method and a reference inter-blade distance detector for a bending machine capable of accurately detecting the actual plate thickness of a workpiece during bending.
Further, the present invention has been made while paying attention to the above-stated conventional disadvantages and the object of the present invention is to provide a bending method and a bending apparatus capable of accurately calculating the relative stroke value of a punch for a target bending angle and carrying out bending with high accuracy.
To attain the above object, the invention is a plate thickness detection method for a bending machine causing a punch to make a relative stroke and bending a workpiece mounted on an upper surface of a die cooperatively by the punch and the die, characterized by relatively descending the punch from a reference position away from the die by a reference inter-blade distance; detecting a relative stroke quantity of the punch if a change in a displacement quantity of a displacement gauge provided in the die, always urged upward from a die V-groove, and measuring a distance to a lower surface of the workpiece is detected, or at a predetermined point after the detection, using a ram position detection means and detecting the displacement quantity of the displacement gauge at this time; and subtracting the detected relative stroke quantity from the reference inter-blade distance and adding the displacement quantity of the displacement gauge to the subtraction result, thereby detecting a plate thickness of the workpiece.
Further, the invention is characterized not only by the previously noted features of the invention, but also in that the reference inter-blade distance is a distance between the punch and the die at a top dead center before relatively descending the punch.
Further, the invention is characterized not only by the above-noted features of the invention, but also in that the reference inter-blade distance is calculated by mounting a workpiece having a known plate thickness on the die before actual bending, relatively descending the punch to detect the stroke quantity using ram position detection means and to detect the displacement quantity of the displacement gauge at this time, adding the plate thickness of the workpiece to the relative stroke quantity of the punch and subtracting the displacement quantity of the displacement gauge from the addition result.
To obtain the above object, the invention is a reference inter-blade distance detection method for obtaining a reference inter-blade distance which is a distance between a punch and a die at an arbitrary reference position, characterized by: mounting a workpiece having a known plate thickness on the die; relatively moving the punch to allow the punch to bend the workpiece cooperatively with the die; adding the known plate thickness to a stroke quantity of the punch at this time and subtracting a displacement quantity of a displacement gauge, provided in the die and detecting a distance from an upper surface of the die to a lower surface of the workpiece, from the addition result, thereby detecting the reference inter-blade distance.
To attain the above object, the invention is a plate thickness detector for a bending machine causing a punch to make a relative stroke and bending a workpiece mounted on an upper surface of a die cooperatively by the punch and the die, characterized by comprising: a displacement gauge provided in the die, always urged upward from a V-groove of the die, and measuring a distance from the upper surface of the die to a lower surface of the workpiece; ram position detection means for detecting a relative stroke quantity of the punch to the die; and a plate thickness arithmetic operation section calculating a plate thickness of the workpiece from a reference inter-blade distance which is a distance between the punch and the die, the distance being input or stored in storage means, a displacement quantity measured by the displacement gauge and the relative stroke quantity of the punch detected by the ram position detection means, and characterized in that the plate thickness arithmetic operation section detects the relative stroke quantity of the punch using ram position detection means at a point at which descent of the workpiece is detected by the displacement gauge or a predetermined point after the point after the punch is relatively descended from a position away from the die by the reference inter-blade distance, detects the displacement quantity of the displacement gauge at this time, and detects the plate thickness of the workpiece by subtracting the detected relative stroke quantity from the reference inter-blade distance and adding the displacement quantity to the subtraction result.
Further, the invention is characterized not only by the above-noted features of the invention, but also in that the reference inter-blade distance is a distance between the punch and the die at a top dead center before relatively descending the punch.
Further, the invention is characterized not only by the above-noted features of the invention, but also by, after a workpiece having a known plate thickness is mounted on the die before actual bending and the punch is relatively descended to detect the stroke quantity using the ram position detection means and to detect the displacement quantity of the displacement gauge at this time, further comprising a reference inter-blade distance arithmetic operation section for adding the plate thickness of the workpiece to the relative stroke quantity of the punch and subtracting the displacement quantity of the displacement gauge from the addition result, thereby calculating the reference inter-blade distance.
To attain the above object, the invention is a reference inter-blade distance detector for obtaining a reference inter-blade distance which is a distance between a punch and a die at an arbitrary reference position, characterized by comprising: a displacement gauge provided to be always urged upward in a V-groove of the die, and measuring a distance from an upper surface of the die to a lower surface of a workpiece; ram position detection means for detecting a relative stroke quantity of the punch; and a reference inter-blade distance arithmetic operation section, after a workpiece having a known plate thickness is mounted on the die and the punch is relatively moved to allow the punch to bend the workpiece in cooperation with the die, for adding the known plate thickness to a stroke quantity of the punch at this time and subtracting a displacement quantity of the displacement gauge from the addition result, and thereby detecting the reference inter-blade distance.
To attain the above object, the invention is a bending method for directly detecting a relative stroke value of a punch to a die using a vertically movable displacement gauge provided in the die and protruded from a V-groove of the die, and for controlling a relative stroke of the punch, characterized by: inputting various conditions including workpiece conditions, die conditions and a target bending angle; obtaining a corresponding relative stroke value of the punch based on the input target bending angle; causing the punch to make the relative stroke by the relative stroke value, and bending the workpiece cooperatively by the punch and the die; actually measuring a bending angle of the bent workpiece; and correcting the relative stroke value based on the actually measured bending angle and the target bending angle.
To attain the above object, the invention is a bending apparatus for directly detecting a relative stroke value of a punch to a die using a vertically movable displacement gauge provided in the die and protruded from a V-groove of the die, and for controlling a relative stroke of the punch, characterized by comprising: input means for inputting various conditions including workpiece conditions, die conditions and a target bending angle; stroke value calculation means for obtaining a corresponding relative stroke value of the punch based on the input target bending angle; bending means for causing the punch to make the relative stroke by the relative stroke value, and bending the workpiece cooperatively by the punch and the die; angle measurement means for actually measuring a bending angle of the bent workpiece; and correction means for correcting the relative stroke value based on the actually measured bending angle and the target bending angle.
To attain the above object, the invention is a bending method for directly detecting a relative stroke value of a punch to a die using a vertically movable displacement gauge provided in the die and protruded from a V-groove of the die, and for controlling a relative stroke of the punch, characterized by: inputting various conditions including workpiece conditions, die conditions and a target bending angle; obtaining the relative stroke value of the punch corresponding to the input conditions from data stored in a database in advance or a theoretical expression based on an experiment; causing the punch to make the relative stroke by the relative stroke value, and bending the workpiece cooperatively by the punch and the die; actually measuring a bending angle of the bent workpiece; and if a difference between the actually measured bending angle and the target bending angle is not within a tolerance, correcting the data stored in the database based on the difference; correcting the relative stroke value based on the corrected data; further bending the workpiece based on the corrected relative stroke quantity; and repeating correcting the data and further bending the workpiece until the difference between the actually measured bending angle and the target bending angle falls within the tolerance.
Further, the invention is characterized not only by the above-noted features of the invention, but also in that if the data in the database is to be corrected, the data is corrected by displacing the data by the difference between the actually measured bending angle and the target bending angle.
Further, the invention is characterized not only by the above-noted features of the invention, but also in that if the data in the database is to be corrected, the data is corrected by displacing the data by a quantity proportional to the difference between the actually measured bending angle and the target bending angle.
To attain the above object, the invention is a bending apparatus for directly detecting a relative stroke value of a punch to a die using a vertically movable displacement gauge provided in the die and protruded from a V-groove of the die, and for controlling the relative stroke of the punch, characterized by comprising: input means for inputting various conditions including workpiece conditions, die conditions and a target bending angle; a database storing the relative stroke value of the punch corresponding to the various conditions or an expression for calculating the relative stroke value of the punch corresponding to the various conditions; stroke value calculation means for obtaining the relative stroke value of the punch corresponding to the input conditions from the data stored in the database; a stroke instruction section for causing the punch to make the relative stroke by the relative stroke value; a comparison determination section for actually measuring a bending angle of the bent workpiece, and determining whether or not a difference between the actually measured bending angle and the target bending angle is within a tolerance; and a data correction section for, it the difference between the actually measured bending angle and the target bending angle is not within the tolerance, correcting the data stored in the database based on the difference, and characterized in that the stroke value calculation means corrects the relative stroke value based on the corrected data, and the stroke instruction section causes the punch to make the relative stroke by the corrected relative stroke value, thereby repeatedly correcting the relative stroke value and causing the punch to make a stroke by the stroke instruction section until the difference between the actually measured bending angle and the target bending angle falls within the tolerance.
Further, the invention is characterized not only by the above-noted features of the invention, but also in that the data correction section corrects the data by displacing the data by the difference between the actually measured bending angle and the target bending angle.
Further, the invention is characterized not only by the above-noted features of the invention, but also in that the data correction section corrects the data by displacing the data by a quantity proportional to the difference between the actually measured bending angle and the target bending angle.
To attain the above object, the invention is a bending method for directly detecting a relative stroke value of a punch to a die using a vertically movable displacement gauge provided in the die and protruded from a V-groove of the die, and for controlling a relative stroke of the punch, characterized by: inputting various conditions including workpiece conditions, die conditions and a target bending angle; obtaining the relative stroke value of the punch corresponding to the input target bending angle from a stroke value-to-angle relationship stored in a database in advance; causing the punch to make the relative stroke by the relative stroke value, and bending the workpiece cooperatively by the punch and the die; measuring a bending load for a certain stroke value before a stroke value reaches a target stroke value, comparing the measured bending load with the stroke value-to-angle relationship stored in the database in advance, and correcting the stroke value-to-angle relationship stored in the database; correcting the target stroke value from the corrected stroke value-to-angle relationship; and bending the workpiece using the corrected stroke value-to-angle relationship as a target.
To attain the above object, the invention is a bending apparatus for directly detecting a relative stroke value of a punch to a die using a vertically movable displacement gauge provided in the die and protruded from a V-groove of the die, and for controlling a relative stroke of the punch, characterized by comprising: input means for inputting various conditions including workpiece conditions, die conditions and a target bending angle; a database storing the input various data, a stroke value-to-angle relationship and a stroke value-to-load relationship both obtained in advance; stroke value calculation means for obtaining the relative stroke value of the punch corresponding to the target bending angle from the stroke-value-to-angle relationship stored in the database; a stroke instruction section controlling driving means so as to cause the punch to make the relative stroke for the obtained relative stroke value; load detection means for detecting a bending load at a certain stroke position until a stroke value reaches the target stroke value; and a stroke value-to-angle correction section for correcting the stroke value-to-angle relationship stored in the database based on the bending load detected by the bending load detection means, and characterized in that the stroke value calculation means obtains a new relative stroke value from the stroke value-to-angle relationship corrected by the stroke value-to-angle correction section.
To attain the above object, the invention is a bending method for causing a punch to make a relative stroke based on input bending data including workpiece conditions, die conditions and bending conditions, for directly detecting a relative stroke value of the punch to a die using a vertically movable displacement gauge provided in the die and protruded from a V-groove of the die, and for controlling the relative stroke of the punch, characterized by: measuring a before-bending plate thickness of the workpiece; calculating a spring back quantity of the workpiece based on the measured before-bending plate thickness of the workpiece and the bending data; calculating an insertion angle based on the calculated spring back quantity; calculating the relative stroke quantity of the punch for bending the workpiece for the insertion angle; calculating a radius of curvature of the workpiece right under the punch if the workpiece is bent for the insertion angle; calculating an after-bending plate thickness of the workpiece when the workpiece has been bent, based on the calculated radius of curvature of the workpiece and the before-bending plate thickness of the workpiece; calculating a final stroke value of the punch based on the before-bending plate thickness of the workpiece, the after-bending plate thickness of the workpiece and the insertion angle; and relatively moving the punch to obtain the final stroke value and thereby bending the workpiece while monitoring the stroke using the displacement gauge.
To attain the above object, the invention is a bending apparatus for causing a punch to make a relative stroke based on bending data including workpiece conditions, die conditions and bending conditions input by input means, for directly detecting a relative stroke value of the punch to a die using a vertically movable displacement gauge provided in the die and protruded from a V-groove of the die, and for controlling the relative stroke of the punch, characterized by comprising: plate thickness measurement means for measuring a before-bending plate thickness of the workpiece; spring back quantity arithmetic operation means for calculating a spring back quantity of the workpiece based on the measured before-bending plate thickness of the workpiece and the bending data; insertion angle arithmetic operation means for calculating an insertion angle based on the calculated spring back quantity; stroke arithmetic operation means for calculating the relative stroke quantity of the punch for bending the workpiece for the insertion angle; workpiece radius-of-curvature arithmetic operation means for calculating a radius of curvature of the workpiece right under the punch if the workpiece is bent for the insertion angle; plate thickness arithmetic operation means for calculating an after-bending plate thickness of the workpiece when the workpiece has been bent, based on the calculated radius of curvature of the workpiece and the before-bending plate thickness of the workpiece; final stroke arithmetic operation means for calculating a final stroke value of the punch based on the before-bending plate thickness of the workpiece, the after-bending plate thickness of the workpiece and the insertion angle; and a stroke instruction section for relatively moving the punch based on the final stroke value and bending the workpiece while monitoring the stroke using the displacement gauge.